Currently, the majority of therapeutic and diagnostic agents are administered to patients systemically. Unfortunately, current delivery methods can have several disadvantages including reduced efficacy of therapeutics as well as side effects due to, for example, drug activation at non-target sites in a patient. In an effort to address some of these drawbacks, targeting delivery of nanoparticles associated with diagnostic and therapeutic agents presents a promising new mode of drug delivery. For some drug delivery methods, nanoparticles, such as liposomes, can target cell surface receptors using a targeting agent attached to the surface of the liposome. For example, the αvβ3 integrin receptor is commonly up-regulated on activated endothelial cells and can be targeted by incorporating a suitable RGD ligand to the surface of a nanoparticle. (Dubey et al., “RGD-modified liposomes for tumor targeting” in Amiji, M. M., Ed. Nanotechnology for Cancer Therapy, CRC Press (2007), pp. 643-661).
While there have been some recent advancements in developing targeted drug delivery methods, there is still a need for further improvements. For instance, methods for transforming nanoparticles to targeted nanoparticles are limited and generally provide inadequate flexibility for modifying the nanoparticles. In addition, compounds that can be used to modify nanoparticles do not allow for adequate ranges of functionality for changing, for example, nanoparticle surface characteristics or diagnostic compatibility. The present invention addresses these and other needs.